Vaccine breakthrough stops cancer returning in trial

Personalized mRNA Vaccine Combined With Immunotherapy Tested in Melanoma Patients

A personalized vaccine developed by Merck & Co, known as MSD outside the United States, and Moderna was administered with the immunotherapy drug pembrolizumab to patients with high-risk melanoma following surgery. The companies reported that the combination extended the period during which patients remained free of cancer recurrence compared with pembrolizumab alone.

The announcement, issued on 19 August 2026, described results from a phase 3 trial involving more than 1,000 participants with stage 2, 3 or 4 melanoma. Patients in the trial had either large localized tumours or disease that had already spread to distant sites. The firms stated that the combined regimen reduced the risk of the cancer returning or spreading to other organs, although the duration of benefit remains to be determined from longer follow-up.

The vaccine, designated Intismeran, is produced using messenger RNA technology. After surgical removal of a tumour sample, its DNA is sequenced to identify mutations specific to that patient’s cancer. The resulting vaccine is designed to direct the immune system against any remaining cells carrying those mutations. Pembrolizumab, marketed as Keytruda, is already approved for several cancer indications and functions by blocking the PD-1 pathway.

Prof Peter Johnson, National Clinical Director for Cancer at NHS England, told BBC Radio 4’s Today programme that the approach differs from existing immune therapies because it provides a specific target rather than broadly activating the immune system. He described the data as an important advance and noted that the NHS is preparing infrastructure to deliver similar treatments.

Merck and Moderna indicated they are conducting additional trials of comparable personalized vaccines in lung, bladder and kidney cancers. Moderna chief executive Stephane Bancel called the melanoma findings a pivotal moment in cancer research. Share prices of both companies rose following the announcement.

Independent specialists emphasised that the results are interim and have not yet undergone peer review. Dr Talisia Quallo, head of prevention and early detection at Cancer Research UK, stated that the data show promise but require full evaluation once complete results are available. She added that continued funding is necessary to develop personalised options that may allow patients to live longer.

Dr Lennard Lee, consultant medical oncologist and associate professor at the University of Oxford, said the trial supplies proof of principle that personalised cancer vaccines can be effective and that the findings have implications beyond melanoma. Detailed results are scheduled for presentation at a medical conference in October.

Any future use of the regimen on the NHS would require regulatory authorisation by the Medicines and Healthcare products Regulatory Agency and subsequent health technology assessment by the National Institute for Health and Care Excellence. The companies have not disclosed the precise length of follow-up or the absolute reduction in recurrence risk at this stage.